1. Field of the Invention
The present invention relates to a composition for use in compression refrigeration and to a lubrication method using the composition. More particularly, the present invention relates to a composition for use in compression refrigeration making use of a refrigerant containing a C1-C8 hydrocarbon, and to a lubrication method using the composition.
2. Description of the Related Art
A refrigeration cycle of a refrigerator such as a compression-type refrigerator including a compressor, a condenser, an expansion valve, and an evaporator is generally designed such that a liquid mixture of a refrigerant an a lubrication case oil circulates in the closed system. In such a compression-type refrigerator, dichlorodifluoromethane (R-12) and chlorodifluoromethane (R-22) have conventionally been employed as a refrigerant in many cases, and a variety of mineral oils and synthetic oils have also been used as a lubrication base oil. However, chlorofluorocarbons such as R-12 and R-22 involve the risk of inviting environmental pollution such as destruction of the ozone layer existing in the stratosphere. Therefore, use of chlorocarbons has come to be more strictly restricted throughout the world. As substitutes therefore, hydrogen-containing fluoro-compounds such as hydrofluorocarbons and hydrochlorofluorocarbons have recently become of interest. Although the hydrogen-containing fluoro-compounds, particularly hydrofluorocarbons led by 1,1,1,2-tetrafluoroethane (R-134a), will not destroy the ozone layer, their long lives in the atmosphere invite some concern about possible contribution to the greenhouse effect. Therefore, a variety of hydrocarbons, inter alia, C1-C8 hydrocarbons, have now come to be studied, as they are free from such problems.
However, when a lubrication base oil prepared from a mineral oil or alkylbenzenexe2x80x94which are conventionally used quite commonlyxe2x80x94is used in a compression-type refrigerator in which hydrocarbons are used as a refrigerant, the refrigerant completely dissolves in the lubrication base oil to reduce the viscosity of the lubrication base oil. As a result, lubrication performance becomes insufficient to reduce antiwear effects, or sealing materials incorporated in the circulation system for the refrigerant degrade to make the sealing effect poor, which may prevent consistent use of the refrigerator over a prolonged period. Particularly in the case in which a capillary tube serves as an expansion valve, there is a strong tendency of sealing effect becoming poor.
The present invention was made in consideration of the above situation, and an object of the present invention is to provide a composition for use in compression refrigeration, which composition exhibits excellent characteristics as a lube oil for compression-type refrigerators, or refrigerating cycles, which incorporate a refrigerant containing a hydrocarbon as the principal ingredient, thus ensuring a prolonged life of the apparatus while reducing wear thereof, and which composition further improves refrigeration efficiency. Another object of the present invention is to provide a lubrication method making use of the composition.
The present inventors carried out extensive studies, and found that when a hydrocarbon compound having predetermined properties or a predetermined formula is used as a lubrication base oil, the aforementioned objects of the present invention can be effectively attained, leading to completion of the invention.
Accordingly, in a first aspect of the present invention, or as first invention, there is provided a composition for use in compression refrigeration comprising
(A) a refrigerant containing a C1-C8 hydrocarbon as the principal ingredient, and
(B) a lubrication base oil primarily formed of a hydrocarbon compound whose non-aromatic-group unsaturation degree is not more than 10% and whose kinematic viscosity is not less than 5 mm2/s.
In a second aspect of the present invention, or as a second invention, there is provided a composition for use in compression refrigeration comprising
(A) a refrigerant containing a C1-C8 hydrocarbon as the principal ingredient, and
(C) a lubrication base oil whose primary component is a polyalkylene glycol derivative represented by the following formula (I):
R1O-(PO)a-(EO)b-R2xe2x80x83xe2x80x83(I)
wherein each of R1 and R2, which may be identical to or different from each other, represents a hydrogen atom, a C1-C10 alkyl group, or a C2-C10 acyl group; PO represents an oxypropylene group, EO represents an oxyethylene group, and a and b are numbers not less than 0 which satisfy the relation 2xe2x89xa6a+bxe2x89xa680; wherein
1) in the case in which R1 and R2 are both hydrogen atoms,
1xe2x89xa610Xxe2x89xa68xe2x80x83xe2x80x83(II)
wherein X represents a mole fraction of PO in the molecule, and is equal to a/(a+b)
2) in the case in which only one of R1 and R2 is a hydrogen atom,
1xe2x89xa610X+Y/4xe2x89xa69xe2x80x83xe2x80x83(III)
wherein X has the same meaning as defined above, and Y represents a sum of the carbon numbers of R1 and R2; and
3) in the case in which neither R1 nor R2 is a hydrogen atom,
3xe2x89xa610X+Yxe2x89xa610xe2x80x83xe2x80x83(IV)
wherein X and Y have the same meanings as defined above; the lubrication base oil having a kinematic viscosity of 5-200 mm2/s at 100xc2x0 C.
In a third aspect of the present invention, or as a third invention, there is provided a method for lubricating compression refrigerators making use of a composition falling within the scope of either one of the above-described aspects.